aco/ngg: Add shader query support to NGG GS.

In each GS thread, we calculate the number of "real" primitives that
were emitted (points, lines, triangles, not strips). Then we
accumulate the number of "real" primitives emitted by the
entire threadgroup in GDS.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <!6964>